The present invention generally relates to fluid pumps and more particularly relates to pump shaft assemblies using eccentric elements.
Eccentric arrangements of this type are used in many ways for the conversion of rotary motions in linear motions, and they are especially well suited for the employment in radial piston pumps. DE 196 36 508 A1 discloses an eccentric arrangement which is used in a radial piston pump for the delivery of brake fluid in controlled automotive vehicle brake systems. The principal operation of pumps of this type involves that an electromotively driven eccentric shaft drives at least two pistons moving in opposite directions by way of the eccentric. To prevent the eccentric shaft from dragging on the drive-side ends of the pistons, a radial bearing is mounted on the eccentric of the drive shaft which follows the radial movements of the eccentric, but is stationary with respect to the drive-side ends of the piston. The radial bearing is designed with a bearing bushing that is open on either side in an axial direction or embraces the eccentric pin on one side, with the result that the radial bearing fixed to the eccentric in the eccentric arrangement described above is secured axially in one direction only, or is not secured at all.
DE 196 32 167 also describes an eccentric arrangement, wherein a radial bearing slipped onto an eccentric ring is also fixed only axially in one direction. Due to vibrations caused in the pumping operation there is the risk that the bearings displace from their position.
An object of the present invention is to configure an eccentric arrangement so that axial displacement is encountered to a minimum extent only, or is prevented at all.
The invention of the eccentric arrangement generally includes designing the bearing bushing of the radial bearing, that is arranged at the eccentric ring, as a cage in such a way that the radially directed lateral walls of the bearing bushing embrace the end surfaces of the eccentric ring. It is a basic advantage of the present invention that the degree of axial freedom of motion of the bearing is limited to a necessary minimum. This is achieved in that the inside surfaces of the radially directed lateral walls of the eccentric bearing may move into abutment on the end surfaces of the eccentric ring in both axial directions. This safeguards that free displacement of the eccentric bearing is prevented.
In a preferred embodiments, it is advisable to reduce the friction between the end surfaces of the eccentric ring and the inside surfaces of the radially oriented lateral walls of the bearing bushing. When the inside surfaces of the radially oriented lateral walls of the bearing bushing are configured as abutment surfaces, friction may be reduced considerably. To this end, the present invention proposes providing the abutment surfaces with a smooth surface by grinding or coating them. As a coating, plastic material or a hard, smooth metal layer may advantageously be used. For a further reduction of friction, favorably, the end surfaces of the eccentric ring can be designed like the abutment surfaces of the bearing bushings.